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THE AM BULLETIN BOARD => Technical Forum => Topic started by: w9jsw on January 19, 2019, 01:51:04 PM



Title: Another 813 Build
Post by: w9jsw on January 19, 2019, 01:51:04 PM
In this thread

http://amfone.net/Amforum/index.php?topic=44480.0

Tom, K1JJ made me an offer I could not refuse, in conjunction with Phil, AC0OB who offered the perfect iron for the build at flea market prices. I had decided to build a 8000 modulated by a pair of 811's mainly due to the cost of the 813 tubes and the lack of a suitable 2Kv power supply. Both of these issues were now resolved, so why not build the big rig!

As we start out I am going to outline my thoughts on how I will approach this build, subject to the vast knowledge of this board to help me "get it right". I have most of the parts in hand or on a truck somewhere.

The phases will be as follows:

Physical design combined with power supply build
RF Deck build
Modulator build

I plan to eventually have an existing Digital VFO (https://www.theladderline.com/node/37) driving a 20W SS amplifier/LPF (QRP-Kits) to drive the RF deck. I may use my Yaesu 757GXII in the interim if I decide to start the RF testing prior to assembling the SS components. For the audio, I will build the mosfet driver that Tom suggested. I have not decided if I will lay it out on a PCB or build it as he did. I plan to drive the audio chain with a combination of RPi 3B+ using some open source audio DAW tools. My work here is documented in another thread.

So that is the preamble...


Title: Re: Another 813 Build
Post by: w9jsw on January 19, 2019, 02:22:14 PM
The physical layout will hopefully comprise a 6ft tall old buzzardly rack that began its life as a Motorola communications rack. It has a door and some nice silver louvers that will nicely dress it up. I just have to convince the plant guys at work that it will be better to let me have it rather than sending it to the crusher. This rack will allow me to put the transmitter components facing out and have the door on the back to avoid wayward cats/grandsons from being fried. I am not yet sure how I will place the supply components in the rack until I get some time to measure them all and see how to get them placed. I have not decided if I will paint it or leave it with its natural patina. It is that not so likable Motorola tan color.

My objective is to build this power supply in a way that I can disconnect the supply from this rig and directly plug it into my Drake L4B Linear that was purchased sans supply. I have the same power cable that Drake used that will allow me to build it to be electrically compatible (except hardwired for 220V only). That way I can just reach over and unplug the PS and plug it into the Drake using the Drake switches to turn it on. I know I could make it fancy and switchable but I really don't see the need and this is just so simple to do it this way. I have all of the Cinch Jones connectors. I am going to make one change - no Millen HV connectors. I am going to use RP-BNC high voltage connectors.

The power supply iron comes from a Gates BC-1T. I will have the transformer, the 8uf oil cap and the choke. I bought 2 more 32uf 4500V oil caps so will have a total of 72uf of filter capacitors. Gonna need a substantial soft start for that much capacitance. I have not decided on a design yet. I have the supply shown in the attached schematics, but will be re-drawing the supply so show the partitioning and component groupings. Going to also as a variac into one leg of the 240V to allow me to control the overall voltage.

Trying to decide if I should make a small control chassis to house the HV meter, switching and screen/bias supplies or if I extend the size of the RF Deck facepate and put the primary supply components there. Taking a look at the size of the screen power trans and the filament transformer, I don't think the RF deck has enough space and they have to be on top. The bias supply is small enough to be under the chassis. Even using my planned 17x17x4 chassis, there is just not enough space I fear. Have to think about that.

Tom, I need to see a pic or get a description of the diode block. I plan to use 15 of the 6A10 diodes per leg. I would like to see how you laid these out and the use of the fuse wires that have protected the strings from disaster as you wrote in some of your threads. I assume it is on plexiglass on ceramic standoffs but the specifics are not firm in my mind.

John


Title: Re: Another 813 Build
Post by: Opcom on January 19, 2019, 06:52:52 PM
No sense in cramming things in making it hard to work on.
A big transmitter should be big, just as happy chair is happy.


Title: Re: Another 813 Build
Post by: K1JJ on January 19, 2019, 09:59:53 PM

Tom, I need to see a pic or get a description of the diode block. I plan to use 15 of the 6A10 diodes per leg. I would like to see how you laid these out and the use of the fuse wires that have protected the strings from disaster as you wrote in some of your threads. I assume it is on plexiglass on ceramic standoffs but the specifics are not firm in my mind.

John


John,

Sounds like a nice plan!  Take a lot of pictures and post them.

It will be fun to watch the rig come together. I am excited that you will be trying to duplicate the RF  layout of Chuck's rig.  Your rig will have evolved by 2-3 builds. IE, it would have taken you several homebrew rigs before you discovered and employed these quality parts and advanced homebrew AM techniques on your own.  You have covered everything from the MOSFET audio driver, computer audio processing, digital RF drive, stiff HV supply, excellent RF parts and layout, commercial iron and big modulators - big audio to RF ratio... nice frickin rig!

I especially like that you listen to advice from others here and actually go out and do it. A more stubborn ham (like me) will do some things his way and regret it later...  ;D


The HV diode stack:

It's just a rectangular piece of Plexiglas mounted on four ceramic pillars.   Some guys use green G-10? fiberglass which looks very professional.  The diodes are mounted in two 15 diode lines. Drill 30 holes  for 15 diodes  and another 30 holes for the other 15 diodes.  Connect them together and solder the leads.   You can lay them out any way that looks pretty as long as the two legs are spaced apart by a couple of inches to avoid dust arcing, etc.    I like the look when the individual diodes are laid side by side instead of in a line.  

The HV fuses:  Big commercial vacuum HV  fuses are expensive... so I mounted  two ceramic pillars spaced 2"-3" apart, and at least 2" high.    Strip a piece of RG-213 shield wire (the outer braid) or equivalent. This is very fine wire. Place 1 to 2 strands in parallel to bridge the gap of the two ceramic pillars.  Use one fuse in series with the stack junction -  at the fullwave diode output just before the filter CHOKE.   You are using choke input so this will give some surge reduction. This assumes you decided to put the choke in the + lead, not the xfmr CT as mentioned earlier in a post.

Bear in mind when a fuse blows, the wire will probably flame an arc a few inches around it and below it... and above it. Mount the fuse in the clear and away from the diodes!  

You will know how many strands to use by experience. Start with ONE strand and if it blows from normal operation, then add another strand.   Bear in mind that these fuse wires can fatigue after a lot of HARD turn-on surges, so if one blows during normal operation after a few months, this probably means to add another strand.   You COULD use the wire/current tables to estimate wire size needed, but trial and error works just as well.  Your step-start will be important for your planned 72 uF of capacitance. A very slow step-start may mean no fuse fatigue problems at all.

The HV fuse definately works. I've had direct shorts for various reasons in the several rigs it feeds and never lost a diode stack in at least 25 years now.  But when the HV fuse does blow, it will leave a bit of soot on the pillars, depending on the intensity. Generally, the 240 breaker will pop at the same time as the HV fuses blows. Sometimes the fuse blows and the 240V breaker  does not.  This is what you want to see.  Coupled with the 25 ohm HV series resistor, we have an overall failsafe system.

BTW, my 4X1 rig HV supply uses three strands of RG-213 braid and has remained intact for a few years now. (140 uF @10 KV, 30 A choke)   Probably cuz I haven't been on the air...  ;)


T


Title: Re: Another 813 Build
Post by: w9jsw on January 20, 2019, 08:37:40 AM
Thanks for the diode stack info. Got it laid out on paper. Will get a piece of plexi this week and get it built.

I have decided build a power control center. Here is how it will work.

240v is supplied to the HV unit and up thru the control cable to the cinch-jones connector. It goes into the L4B amp or control head then back out to the supply as switched 240v. I plan to put a relay in the HV unit to bypass this current path so that the voltage going back is low current. This is a common update for L4B supplies to allow for reduced current on the switches. This will also insure that I am not carrying full current for the trans up and down the cable. The L4B transformer is 700VA. This Gates one is at least 1500VA. The 240 will have circuit breakers and soft start in the HV unit.

Should I have the control head get a separate 120V or should I send a neutral up the cable and split the filament and supplies across the load and run it all off of 1 240v feed? The schematic shows sending ground on pin 7 but no neutral. Pin 8 is not connected in the L4B supply but it is grounded on the L4B amp chassis. I could lift that ground and pass neutral on pin 8. My house is build according to the 4 wire code so my neutral and grounds are separate except at the transformer pole where they are bonded together.  

I think this will be safe. My reasoning is that I am the one that will be using my HV with my amp. There would be concern if someone took my HV supply and plugged it into another amp. The concern being that the neutral and grounds would be bonded at the amp. My amp being plugged into another L4B supply would be no concern at all, I believe.

Thoughts?

The control head will have fused switching for filament 120V. I plan to use those nice computer power connectors to feed the 120 voltage out of the control head up to each chassis (mod and rf) to the filament transformers. I will have 2 RP-BNC connectors to loop the HV from the HV unit and feed it out to the mod deck. Then 2 more connectors to loop it from the mod deck to the RF deck. I can buy pre-made HV cables with nice insulated ends. I will also have an HV meter on the control head so there will be a resistor string there to drop the voltage to a measurable value. Variac on one leg of the HV input feed to control overall HV output.

The fused screen and bias supplies will be built entirely on the control unit chassis, including the VR-75 tube and small variac. See schematic for locations where the split occurs (the split at VR75 is not correct on the schematic). The meters for these supplies will be located on the RF front panel.

I plan to have a BIG RED SWITCH on the primary 240V feed mounted prominently somewhere that can shut the whole mess down. I don't want to have to be reaching to unplug something if the main relay decides to fuse closed or some other major failure.

Well, I think that is the plan so far. I will revise my schematics to reflect this partitioning plan. I like my schematics to be a good roadmap for the build and a good reference if I have to go back 5-10 years later to repair something.

John


 


Title: Re: Another 813 Build
Post by: PA0NVD on January 20, 2019, 01:56:18 PM
I always use the HV fuse of magnetron ovens, they are ok upto approx 3 kV, small and enclosed in an isolating cartridge. And when they blow, i do the same as you did, use thin wire to repair the fuse (if you don't have spares or a shop closeby)


Title: Re: Another 813 Build
Post by: W2PFY on January 20, 2019, 04:19:41 PM
Quote
I had decided to build a 8000 modulated by a pair of 811's

Is this going to be a push pull circuit? I built an amp using 8000's way back around 1978 and it worked great in push pull. It had more output than 810's in the same circuit. 8000's are quite rare so if you run out of 8000's, 810's are not hard to find and will most likely other than bias adjustment, will be a drop in replacement.

Is your power supply going to be cap input? That's a lot of capacitance and could result in an electrical explosion if something were to short out.  The link below has fuses and holders.

https://www.ebay.com/sch/i.html?_from=R40&_trksid=m570.l1313&_nkw=Microwave+Oven+High+Voltage+Fuses&_sacat=0 (https://www.ebay.com/sch/i.html?_from=R40&_trksid=m570.l1313&_nkw=Microwave+Oven+High+Voltage+Fuses&_sacat=0)

There are other fuses listed at higher ratings in amperes by looking around eBay but most are rated at 5 KV.

I cannot express forcefully enough to make every effort to make sure that your capacitors are discharged completely and that a ground shunt or short be in place at many points where lethal voltage may be present! Just shorting something out with a screw driver is not enough! The shorting mechanism need to be in place throughout while high voltage repairs are being made!


Title: Re: Another 813 Build
Post by: w9jsw on January 20, 2019, 05:21:39 PM
Points noted on the danger. Power supply is choke input as shown in the attached 813 schematic.

Do you have an example of a shorting mechanism that is safe when in operation?

Here is what I am building - http://www.amwindow.org/tech/htm/813/813.htm

I _was_ building an 8000 rig...



Title: Re: Another 813 Build
Post by: PA0NVD on January 20, 2019, 07:01:42 PM
The Collins KWS1 uses a leave spring that shorts the HV as soon as the top plate is removed. Very simple and safe system. If someone has a KWS1, he can make a pic of it.


Title: Re: Another 813 Build
Post by: W2PFY on January 20, 2019, 07:52:08 PM
Quote
Do you have an example of a shorting mechanism that is safe when in operation?


Commercial systems use an interlock system. I'll get back to you with an idea or two sometime tomorrow. Too tired tonight to strain the brain  ;D ;D

I guess I need to read more closely to understand what you are doing? All I had to do is read :D :D


Title: Re: Another 813 Build
Post by: KD6VXI on January 20, 2019, 09:29:38 PM
I use perf board from....  RadioShack.com for my diode stacks.

Less drilling 😇

--Shane
KD6VXI


Title: Re: Another 813 Build
Post by: Opcom on January 21, 2019, 01:10:41 AM
I suggest a 4 wire 240V cable to the power supply, then run 120V, neutral, and GND to the controller from a jones connector etc. on the power supply. You can be sure it's all un-powered whenever you disconnect the single 240V plug, and since the control has a special plug, it can't be plugged into a 120V outlet by error.

The reason I suggest this is because I used to run a separate 120V power cord to the control box and got a very nasty surprise while working on the unplugged Tucker transmitter, as the station control was still plugged in and supplying 120V to the transmitter in a roundabout way. The worst part was not the shock, but the large cut on my arm as I jerked it out of the bowels of the transmitter.


Title: Re: Another 813 Build
Post by: DMOD on January 21, 2019, 02:22:41 AM
First thing you know John is that next you'll be feeding the output of the 813 into a setof parallel 833s or 4-400s. ;D

Phil - AC0OB


Title: Re: Another 813 Build
Post by: w9jsw on January 21, 2019, 06:37:36 AM
Is there no end to this madnesss?  ;D

Great suggestion, Patrick. I will incorporate it. That way no mods to the L4B.



Title: Re: Another 813 Build
Post by: w9jsw on January 25, 2019, 06:37:14 AM
385 pounds of iron arrives today  8)


Title: Re: Another 813 Build
Post by: K1JJ on January 25, 2019, 05:07:44 PM
385 pounds of iron arrives today  8)


And six pounds of 813s, caps and sockets are on the way to you today now that the ice storm is over..

The postal worker wanted to know if I wanted to pay an extra $10 for a "fragile" sticker.  I said no and  figgered it was packed well enough with styro and bubble pack so that the tubes would be FB.    813s are possibly the most rugged big transmitting tube ever made.

So what's the latest on the project over the last week?

The most difficult part may be finding a name for your rig. I've had rig naming contests here in the past.  Just so you know..."Fabio", "Dr. Love",   "Dual Quads" and "Rico Suave"  are already taken. Or you could do like most hams and just call it "The 813 AM Rig."     ;D


T


Title: Re: Another 813 Build
Post by: w9jsw on January 26, 2019, 06:41:47 AM
Thank you Tom for keeping your promise on this deal and your help along the way. I would not have taken this leap without support.

Going to do the physical layout of the power supply today, and build the diode array. I assume I should be using the center conductor from some poly RG58 for all voltage interconnect on the supply?

Have electrical connectors showing up to do the interconnects to and from the control panel. Also going to lay out the screen/bias transformers and power supply circuits on the chassis. I have a free-standing supply for the 24v relay power.

Want to thank Phil for delivering the iron. As we were talking in the parking lot, for a fail-safe Phil suggested a large relay that is energized from the line power that holds off a large resistor when on. When line power is removed it is placed across the caps to quickly drain them and keep them shorted. He suggested a 200W one with sufficient resistance to bleed it off quickly. What can I do to reduce the arcing on the relay - some decoupling caps across the relay will not be enough. Going to do a little googling to see what others have done. Guess I could us one of those nice russian spst vacuum caps here as well?

Thoughts?

Also will spend time this morning doing the final schematic for the PS.

Names? Gort is taken also. Was thinking "Lord please don't let this PS kill me" but that is too long.  ???

John



Title: Re: Another 813 Build
Post by: w9jsw on January 26, 2019, 12:45:22 PM
Here are the latest schematics. Reworked the power so it shows the HV unit vs. the power controller. Still have to design a soft start. Suggestions for a KISS approach?

20A or 30A breakers? 30A or 40A main breaker on the panel? Guess I should check the Gates schematic to see what they did.

On edit - the Gates fused at 30A providing 3500W of power at 85% modulation running a pair of 833s driven by a pair of 833s. That works out at ~15A steady state. This transmitter should pull about the same or somewhat less, I would guess. I think I will have breakers at 25A on the HV unit and a 30A electrical circuit. Soft start will help here on the surge current.

Phil gave me the Gates filament transformer also. Looking to see if I should use it. It has multiple 10V filament feeds. What is the rule of thumb on how far the filament transformer should be away from the tubes themselves?

Added the antenna switching and the proposed sequencer order. Please help me here on the initial sequencing plan.

Is it necessary to have the 33K/200W additional R on the supply? It will drain the power at 80ma after the mains are shut off. That is 200W of power at 2.5kV.

Wondering if I should drop the 8uf oil cap. That was the original Gates cap. I have added 64uf of additional capacitance. Why bother with the 8uf can...

After this design session, I still have parts to buy. Thought I was about done... oh well..

John


Title: Re: Another 813 Build
Post by: w9jsw on January 26, 2019, 01:10:20 PM
Forgot the HV fuse...


Title: Re: Another 813 Build
Post by: W2PFY on January 26, 2019, 05:17:32 PM
Quote
He suggested a 200W one with sufficient resistance to bleed it off quickly. What can I do to reduce the arcing on the relay

I think this may be a non issue since you are bleeding off to a resistor and not an inductor.

What value of resistor are you planing on using? Bleeder resistor typically rage from 50 to 100 K depending on how stiff you want the regulation. I always suggest using resistors in parallel to give you a safety margin in the event that one resistor goes open. For example two 100k in parallel to arrive at 50k. 


Title: Re: Another 813 Build
Post by: KK4YY on January 26, 2019, 06:26:05 PM
Quote
...Bleeder resistor typically rage from 50 to 100 K depending on how stiff you want the regulation. I always suggest using resistors in parallel to give you a safety margin in the event that one resistor goes open. For example two 100k in parallel to arrive at 50k. 

I bought a bunch of 200k 2w 5% metal film resistors for use as bleeders. With 200k across a 400v capacitor 0.8w are dissipated, worst case. That's a 2.5:1 safety factor. I parallel units to get the amount of bleed I want. A one-size-fits-all solution.

1 unit, 200k bleed.
2 units, 100k bleed.
3 units, 67k bleed.
4 units, 50k bleed.
5 units, 40k bleed.

Don


Title: Re: Another 813 Build
Post by: w9jsw on January 27, 2019, 08:53:39 AM
Working on the step start part of the circuit.

My transformer is a big Gates transformer. Inrush current is going to be big given that I have 72uf of caps on the secondary. For safety reasons I decided that I will have good old fashion switches to cut off the power. They then feed to a relay where I can switch the HV from either the control head or the L4B Linyaaar amp. This relay is controlled by a 120v feed. After the relay I will have a variac on one or both legs of the feed depending on what I can find. Next in the line is the step start. I have read about them from various uses, mostly on amps with considerably smaller transformers. I think this one needs to be substantial.

I am going to build the step start along these lines. Maybe Phil can help me with estimating the specs on the transformer.

http://amfone.net/Amforum/index.php?topic=41787.msg303932#msg303932

I am going to use the 40H estimate until I can measure the trans. Not sure my little LC tester can go that high.
Caps - 72uf
Sec current - 1.5A
100K Bleeder

TC - R*C =7.2s (a long time)

R = L/TC = 5.55 ohms

Fuse = 1.5*2.5=3.75A

So looks like a 6ohm 200W R in series with a 4A SB fuse?

That TC is really long. If I go to switching HV during a QSO I think I will need a better solution.

Going to drop the 33K extra bleeder. I think I will use the existing 100K bleeder with a mechanical interlock to short out the filter caps if the case is opened.

New schematic. Going to start the PS build this afternoon if I don't get a hernia carrying the iron to the shack in the basement.

John


Title: Re: Another 813 Build
Post by: KD6VXI on January 27, 2019, 10:39:03 AM
Was thinking "Lord please don't let this PS kill me" but that is too long.  ???

John

I've got that power supply in my shop.  Knocked me with 6kv.


--Shane
KD6VXI


Title: Re: Another 813 Build
Post by: w9jsw on January 27, 2019, 11:16:57 AM
I read the post - scary. That is why I am going with RP-BNC as suggested in a reply to that post. No Millen HV for me.

Glad you are ok.

John


Title: Re: Another 813 Build
Post by: K1JJ on January 27, 2019, 11:56:02 AM
Hi John,

Without going into formulas, I'll give you my practical experience on step-starts...

There are many ways to approach this. I personally like keying the HV for transmit/ receive. The goal is to reduce the initial major surge, that capacitor-only supplies can reach  Ö 10, 20, 30+++ amps, depending on the components and voltage level.   The diodes can handle this as well as most capacitors, but it does raise havoc on longevity if pushed to an extreme.

In your favor you are using a big choke input, which will oppose the flow of current as the mag field initially builds. This is a good thing.

Most of the initial charging occurs very quickly, in under a second.  A step start is the best way to add more "cushion" to the surge.  My suggestion is a 5-10 ohm 200 watt resistor that stays in the 240 VAC primary for 1/4 to 1/2 second and then gets bypassed - is about right for your supply.  That 1/4 to 1/2 second can get "buried" with the other functions of sequencer antenna/ driver switching, amplifier key up, etc.  The resistor contactor (and any other associated relays in the 240VAC primary) should be a robust 240VAC type, 24VDC coils, about the size of a lemon with heavy contacts, open frame... you know the type.  No RS 12 V relays.

You will see your AM carrier come up before the step start drops out and then there will a few DB power peak afterwards. You may hear the second click of the relay unless you use some kind of audio delay as I do, to remove all the shack noises on key up. IE, the audio comes on last.

If you make your step start timer variable, you will be able to find a compromise between key-up speed and reasonable current surge. I run this same setup and component values on my own 140 uF, choke input 4KV HV supply.  My total delay is about 3/4 second and the HV supply is barely stressed on key up.  The HV  B+ line fuses also provide protection and a good guide to how hard the system is being stressed.  If the HV fuses fatigue after only a few short days of use, then you need to either increase the fuse rating or decrease the surge startup level.
 
BTW, I will try to get to your other questions later... For now, your question about switching in the additional bleeder after shut down... you already have fixed bleeders on the filter caps, right? Then the extras are a redundant system for safety and is always a good thing if you want to go thru the extra building effort. Most hams don't bother, but if you are extra nervous, then do it.


No, the small 8 uF will just mostly take up space... stick with the two 32 uF beasts. Use it as a spare.


T


Title: Re: Another 813 Build
Post by: w9jsw on January 27, 2019, 07:38:14 PM
ok, SS is now variable using Square D octal timer delay relay driving PB open frame relays for HV on/off and step start resistor engage/disengage. Inexpensive and look robust. I have to run 120V coils however, since I do not have 24V in the HV unit. Schematic getting a bit busy in that part of the sheet.

I think this unit is now going to be separate from the rest so I can move it around to future transmitters and move it if I want to run the L4B. I am re-thinking the full 6ft rack. I may go to a half rack that holds the controller, RF Deck and Modulator. Still trying to decide. I don't have a lot of space in the basement so ease of moving is important. Stuffing the PS components in the bottom of the Motorola rack (if I get it) will make it very cramped and not very serviceable. That transformer and choke are HUGE. Thinking of a roll-about wooden platform with a removable interlocking metal cover that makes it easy to expose and work on the PS unit (power off of course). Kind of like a mover's dolly with a metal cage around it. I can then roll it under my tables to get it out of the way.

Trying to think of a indicator that will illuminate as long as there is potential on the caps. Or I will just mount a second meter on the HV unit. I want a visual indication of it being dead. Otherwise when I open the unit I will kill an interlock switch in the process.

John


Title: Re: Another 813 Build
Post by: K1JJ on January 27, 2019, 08:08:29 PM
ok, SS is now variable using Square D octal timer delay relay driving PB open frame relays for HV on/off and step start resistor engage/disengage. Inexpensive and look robust. I have to run 120V coils however, since I do not have 24V in the HV unit. Schematic getting a bit busy in that part of the sheet.

John


Hi John,

Sounds good on the step start.

For relays: I would recommend staying with 24 VDC coils only - for all station switching.   They are generally quieter and safer than 120VAC coils.

I also have 12VDC available for T/R keying since it is sometimes needed too.

Try some of your AC coil relays and see if they buzz.  I ended up with about (15) 24 VDC coil relays  in my control system, including AC mains contactors. All those relays would be a lot of racket if AC, especially the bigger ones.  Some get mechanical resonances and buzz at 60 Hz. At least that has been my experience.  The first time I knew I didn't like 120 VAC relays was as a Novice switching the Johnson Matchbox ant relay. I blew a hole in the aluminum rear panel.... :-)

BTW, there are lots of cheap 24VDC small switching power supplies on eBAy, etc. I use a few here for 24VDC and 12 VDC. Ya never know when you will need another relay as you add equipment.

Basically I have a 24 VDC T/R keyed wire, running to all rigs. When a rig's panel T/R switch is on, that rig gets keyed and switches its antenna relay, mod and RF PA on, etc.   Simple.

T


Title: Re: Another 813 Build
Post by: DMOD on January 27, 2019, 10:39:25 PM
Hi John,

Here is an inrush circuit that should handle the inrush current for initial charging.

It is a modification of the one that I use on my Henry 2k-4.


Phil


Title: Re: Another 813 Build
Post by: DMOD on January 27, 2019, 10:40:32 PM
Hi John,

Here is an inrush circuit that should handle the inrush current for initial charging.

It is a modification of the one that I use on my Henry 2K-4.


Phil


Title: Re: Another 813 Build
Post by: w9jsw on January 28, 2019, 06:47:57 AM

For relays: I would recommend staying with 24 VDC coils only - for all station switching.   They are generally quieter and safer than 120VAC coils.


OK, all 24V now.

On edit - think I will slap a 2200uF cap across the surge relay coil and not put in the delay relay for now. That should give me around 3/4 of a sec of delay which should be a good starting point. I will make space for the third relay if I need to mess with the TC.

John


Title: Re: Another 813 Build
Post by: w9jsw on January 31, 2019, 12:47:42 PM
Relays are here, going to start construction.

Tomís tubes are here as well!


Title: Re: Another 813 Build
Post by: w1vtp on February 01, 2019, 01:01:34 PM
The Collins KWS1 uses a leave spring that shorts the HV as soon as the top plate is removed. Very simple and safe system. If someone has a KWS1, he can make a pic of it.

So does the Heath SB220/221. Unfortunately, some have, without thinking, removed the cover with the HV on which usually ends up with some destruction of some HV components. Seems to me there should also be an interlock that would remove the primary to the HV xvmr along with the shorting leaf. No. No fuse will act fast enough to protect the HV components.

Al

PS: Forgot to mention that a "glitch fuse" works fast enough. W2DTC has some nice detail on this. Usually made of #30 wire but the Clipperton L uses a pair of carbon comp resistors that works well plus provides an interesting light show should they be violated.

Just check Ken's site and he prefers the light show so he knows that there is a problem. He also uses magnet wire
http://w2dtc.com/w2dtc-class-a-rf-amp/2007-1204-b-plus-glitch-resistors.jpg (http://w2dtc.com/w2dtc-class-a-rf-amp/2007-1204-b-plus-glitch-resistors.jpg)


Title: Re: Another 813 Build
Post by: PA0NVD on February 01, 2019, 01:05:49 PM
Yes, there is also a microswitch swithing the HV off. I tested once and only the HV fuse was the victim, no damage done


Title: Re: Another 813 Build
Post by: w8khk on February 01, 2019, 02:20:31 PM

For relays: I would recommend staying with 24 VDC coils only - for all station switching.   They are generally quieter and safer than 120VAC coils.


OK, all 24V now.

On edit - think I will slap a 2200uF cap across the surge relay coil and not put in the delay relay for now. That should give me around 3/4 of a sec of delay which should be a good starting point. I will make space for the third relay if I need to mess with the TC.

John

If you place a cap across the relay coil, it not only delays the contacts making contact, but it will also hold the relay in for a while and delay the contacts breaking when you go back to receive.  To avoid this, you might want to add a diode in series with the capacitor, charging it while going from receive to transmit to delay the contact closure, but also allowing the contacts to close immediately without the capacitor holding the relay closed.  I used an extra set of contacts in my sequencer to discharge the capacitor through a resistor when the relay opens, such that the delay function is preserved the next time the relay is energized. 


Title: Re: Another 813 Build
Post by: K1JJ on February 01, 2019, 02:44:30 PM
Quote
If you place a cap across the relay coil, it not only delays the contacts making contact, but it will also hold the relay in for a while and delay the contacts breaking when you go back to receive.  To avoid this, you might want to add a diode in series with the capacitor, charging it while going from receive to transmit to delay the contact closure, but also allowing the contacts to close immediately without the capacitor holding the relay closed.  I used an extra set of contacts in my sequencer to discharge the capacitor through a resistor when the relay opens, such that the delay function is preserved the next time the relay is energized.  


Yep, I was thinking the same thing, Rick, but forgot to comment on it.   Before I went with all adjustable delay relays for the sequencer controls, I tried the capacitor/resistor/diode circuit. It worked OK, but it took some messing with to get it perfect.   I've found as you change things and want different timing responses in the shack, the timer relays are a cinch to make things right with a turn of the knob.  

Somewhat elaborate I admit, but with mine, I can independently adjust the attack and release times and keying order - which helped to fine tune my arcing T/R problems with the 4X1 rig. It also controls HV step start, antennas, mod deck, RF keying, audio, mod reactor quenching, etc.

There is a sweet spot in adjustments where the transmitter keys and operates smoothly and near perfect..

Page 8, 9 shows and discusses the sequencer details. It was designed by Jeff, W2NBC:

http://amfone.net/Amforum/index.php?topic=33816.200


T


Title: Re: Another 813 Build
Post by: w8khk on February 01, 2019, 06:25:31 PM

Yep, I was thinking the same thing, Rick, but forgot to comment on it.   Before I went with all adjustable delay relays for the sequencer controls, I tried the capacitor/resistor/diode circuit. It worked OK, but it took some messing with to get it perfect.   I've found as you change things and want different timing responses in the shack, the timer relays are a cinch to make things right with a turn of the knob.  

FB on the adjustable delay relays, Tom.  That certainly is a convenient way to fine-tune the sweet spot.  

I designed an RC time constant sequencer, amplified by a few cheap NPN transistors to drive the relays, thus taking the relay coil variations out of the equation.  I put these on a perf-board under the chassis in my Viking II and Valiant.

Currently I am finishing up the software to do all sequencing with an Arduino Nano ($3) and a relay module with eight optically-isolated SPDT relays ($6) and a 4-line 20-character LCD display ($5) with a couple buttons to configure the desired options.  This allows me to keep several transmitters attached and select the desired combination via a simple menu.  The buttons were two for a buck and the entire shebang is powered by a 5-volt micro-USB cellphone charger.  Can't get much cheaper than that!

Don't want to hijack John's 813 thread, but knowing he is a software jock, this idea might interest him as well.  Real simple to code in C with the Arduino IDE.  Cheaper and simpler than a bunch of RC circuits!


Title: Re: Another 813 Build
Post by: w9jsw on February 01, 2019, 08:12:52 PM
Got my interest, Rick.

There are 2 issues at play here and I am only trying to solve one now. I understand the need for overall sequencing (Fabio II was very illustrating) and the strong desire to have it quite flexible.

The primary engineering issue at hand here is how to safely handle the inrush current on this very large supply properly so that every time I activate it the diodes are protected while those large caps charge. I think this needs to be a fixed TC and absolutely independent of overall sequencing or I will risk PS components and safety. I can't let a mistake or failure on sequencer delay cause the HV PS to blow fuses or arc.

This also under the constraint of having to use one lead of 240v on the input to energize the supply to maintain compatibility with the L4B. 24V coils makes that much more complex.

After looking at all the options, I think I will try Phil's approach. I plan to have the overall HV controlled by a 24v line on the controller that I can drive from the sequencer. And if this idea that Rick has looks good, I will have excellent overall control of the rig.

I also have a mechanical interlock switch that will hopefully only blow the fuse if it is accidentally tripped.

New schematic.

John


Title: Re: Another 813 Build
Post by: w9jsw on February 02, 2019, 10:39:39 AM
Since we are also talking about sequencing - I read the Fabio II thread. What would a good starting approach be? (Ignore my sequencing in the schematic) I have relays for HV, RF drive, PTT (mod and RF Deck keyed at the same time), and antenna. I have not made a provision for screen.

I am thinking about separating the RF Deck and Mod PTT relay mainly because I don't want to run a line from the relay on the mod deck across to the RF deck (see schematic).

Key on

1 - Antenna
2 - PTT (both Mod and RF)
3 - HV
4 - RF Drive
5 - Audio

Key off reverses.

thoughts? Should mod and RF deck be on separate sequences?

John


Title: Re: Another 813 Build
Post by: KK7UV on February 02, 2019, 07:44:30 PM
This is great.  I am following along on your project closely.  I have wanted to build the K1JJ rig for several years but am still on the hunt for the last remaining piece - a dang modulation transformer.

-Steve


Title: Re: Another 813 Build
Post by: K1JJ on February 02, 2019, 09:43:34 PM
Since we are also talking about sequencing - I read the Fabio II thread. What would a good starting approach be? (Ignore my sequencing in the schematic) I have relays for HV, RF drive, PTT (mod and RF Deck keyed at the same time), and antenna. I have not made a provision for screen.

I am thinking about separating the RF Deck and Mod PTT relay mainly because I don't want to run a line from the relay on the mod deck across to the RF deck (see schematic).

Key on

1 - Antenna
2 - PTT (both Mod and RF)
3 - HV
4 - RF Drive
5 - Audio

Key off reverses.

thoughts? Should mod and RF deck be on separate sequences?

John

Hi John,

Yes, Rick's adjustable delay software sequencer will suit you fine.

The sequencing timing you show above is a good starting point.   I use a screen relay in my sequencer keying on the RF deck.  Your mod tubes in triode config do not need screen keying IIRC.  When you test you will see.  My own 4-1000A modulators are tetrode config and do use a screen relay and regulated supply.

I believe I made my TX key and mod key independent.  Reread the Fabio sequencer thread on pages 6,7,8,9,10 to see what I went thru.
There were a lot of changes and experiments before arriving at the best optimization!
http://amfone.net/Amforum/index.php?topic=33816.200

Once running, there may be small screen/grid/plate  meter jumps on key up and unkey that will require some sequencer fine tuning.(assuming it's not caused by parasitics)  I even changed the key up order at times. You will have to test and see.

Bear in mind that some big rigs have no sequencing at all and get away with it FB.  A sequencer is simply another step to making sure the rig operates smoothly and without surges, arcing, etc.  I always use a sequencer for all big rigs here and gain full control of the rig.

Another thing to consider adding is a 5K-7K 100W power resistor that gets switched across the modulation reactor during unkey to quench the arc and dissipate the magnetic field. It gets keyed open during transmit using a vacuum relay. This makes a big difference when it's time to unload the high power audio and protect the mod iron..   Normally the antenna takes the RF deck dumped energy without this kind of relay circuit, but the mod xfmr and mod reactor are not always able to dump it easily into the RF deck and may create spark gap arcs that can be excessive.  During sequencer testing I seem to remember keeping the RF deck on for an instant while the modulator finished dumping its power.

Anyway, you may and may not need these extra features, but now you know what to do if these problems come up.  Think in terms of "where will the dropped power go and what currents will want to soar when I key and unkey?" "Will a different order and timing help solve these problems?" "What will happen if I turn the screen on without the HV?"  "Is it best if the audio keys on last so that the whole modulator chain and RF deck have good loads?"  "Will the RF deck screens stay in safe cutoff if the RF drive comes on before the HV?"    These are good questions to learn from and get you thinking in the right direction.

T


Title: Re: Another 813 Build
Post by: K1JJ on February 02, 2019, 11:17:03 PM
This is great.  I am following along on your project closely.  I have wanted to build the K1JJ rig for several years but am still on the hunt for the last remaining piece - a dang modulation transformer.
-Steve


Hi Steve -

Welcome with your first post!

Iron is usually no problem. Put out a "wanted" ad on several of the web ham bulletin boards for broadcast modulation iron, (mod xfmr and mod choke)  500W - 1KW range.  (like QRZ.com, etc.)   There are many old ham AMers - some from the 50's and 60's in its heyday, with this heavy iron in the cellar who will never get around to using it. They'd love to have an enthusiastic homebrewer take it away. Got a strong back?  :-)

Write in the ad you are building a homebrew 813 ham transmitter for 160-20M. (or whatever)  This will inspire the OTs to help you out...

Try and see. I'll bet you find some quickly.   John had the same problem and found it in only a few days right here on this BB.


73,

Tom, K1JJ


Title: Re: Another 813 Build
Post by: KK7UV on February 03, 2019, 06:30:25 AM
Hi Tom.   I am actually not new here.  For some reason I was no longer able to log in with my old user name "stevef" so I didn't see any option but to create a new account.   Anyhow - I will take your advice - Thanks!

Steve   
 


Title: Re: Another 813 Build
Post by: w9jsw on February 06, 2019, 07:39:11 PM
Still ironing out a few details. I was not happy with the mains switch setup. Now have a 3pdt relay with a start-stop no/nc switch. This will give me an auto power off if there is a power glitch. Parts still not all here so no progress on the actual build other than rough layout. Main item to fit just arrived on Monday, a Superior Powerstat. Going to have ability to vary HV from around 1500v on up.

Watched the ARRL video of the Gates bringup with Tron. Noticed they were running the HV at 1800v. Was cool to recognize the same components that I have.

Question on filaments. I have 2 separate transformers or I can use the dual 10v one from the Gates. Is it better to have the filaments trans close to the tubes it feeds or can I mount the dual one and feed the tubes with 2-3 foot leads?


Title: Re: Another 813 Build
Post by: Opcom on February 06, 2019, 08:50:47 PM
Filament transformer leads need be large enough to avoid voltage drop. Otherwise no issues with a remote transformer. I presume you will monitor filament voltages at the socket, so all should be well.



Title: Re: Another 813 Build
Post by: KK7UV on February 06, 2019, 08:54:01 PM
Which MOSFET audio driver are planning to use?


Title: Re: Another 813 Build
Post by: K1JJ on February 06, 2019, 09:13:11 PM

Question on filaments. I have 2 separate transformers or I can use the dual 10v one from the Gates. Is it better to have the filaments trans close to the tubes it feeds or can I mount the dual one and feed the tubes with 2-3 foot leads?

John,

Yes, as Pat says, any length filament leads will do, but if they are too long you may not have enough tap or Variac range for  the fil xfmr to cover the voltage drop. Just a waste of power since 813s take a fair amount of fil juice.

Just be sure to well bypass the RF stage 813 with .01s at the fil pins... and also bypass the modulator tubes at the fils with both audio and RF bypass caps. I see no audio bypasses on the Tesla 300 schematic.   I have run tests without audio bypass caps and did not see much difference in sweep performance, but would hate to think that the extreme highs were getting thru the iron without problems. If anything, bypass both stages well to enhance stability.

Yes, you can use either separate fil transformers or dual windings. Once the RF or audio gets bypassed to ground, the stage doesn't care where the 10 VAC comes from.

T


Title: Re: Another 813 Build
Post by: Opcom on February 06, 2019, 09:16:23 PM
I've got that power supply in my shop.  Knocked me with 6kv.
--Shane
KD6VXI
How are you now BTW? I hope healed up well!!


Title: Re: Another 813 Build
Post by: Opcom on February 06, 2019, 09:44:27 PM

Question on filaments. I have 2 separate transformers or I can use the dual 10v one from the Gates. Is it better to have the filaments trans close to the tubes it feeds or can I mount the dual one and feed the tubes with 2-3 foot leads?

John,

Yes, as Pat says, any length filament leads will do, but if they are too long you may not have enough tap or Variac range for  the fil xfmr to cover the voltage drop. Just a waste of power since 813s take a fair amount of fil juice.

Just be sure to well bypass the RF stage 813 with .01s at the fil pins... and also bypass the modulator tubes at the fils with both audio and RF bypass caps. I see no audio bypasses on the Tesla 300 schematic.   I have run tests without audio bypass caps and did not see much difference in sweep performance, but would hate to think that the extreme highs were getting thru the iron without problems. If anything, bypass both stages well to enhance stability.

Yes, you can use either separate fil transformers or dual windings. Once the RF or audio gets bypassed to ground, the stage doesn't care where the 10 VAC comes from.

T

For low voltage high current filaments a good and very flexible wire is the stuff used by car stereo shops for high power amps. It's made of many fine wires like a welding cable (The #10 may have 500-1000 strands), instead of a few coarse ones like 'mains' wiring. It's cheap too.  Just encouraging overkill..
Its insulation is usually silicone type and not as tough as the 600V stuff, but heat shrink tubing helps.


Title: Re: Another 813 Build
Post by: w9jsw on February 07, 2019, 06:40:27 AM
Which MOSFET audio driver are planning to use?

The one that Tom used on Fabio II.

John


Title: Re: Another 813 Build
Post by: K1JJ on February 07, 2019, 12:13:18 PM
Which MOSFET audio driver are planning to use?
The one that Tom used on Fabio II.

John



This thread:

http://amfone.net/Amforum/index.php?topic=23632.0

(Schematic on webpage above, 3rd post.)


T


Prototype and current PCB:


Title: Re: Another 813 Build
Post by: Opcom on February 07, 2019, 11:31:01 PM
Wasn't there a picture of the power supply of this, like a short rack with a quite large size power transformer sitting in front of it?


Title: Re: Another 813 Build
Post by: KD6VXI on February 08, 2019, 10:54:01 AM
I've got that power supply in my shop.  Knocked me with 6kv.
--Shane
KD6VXI
How are you now BTW? I hope healed up well!!

I'm back working in the shop.  Cost me about 6 weeks of downtime but better than the alternative!  Dirt nap!

Glad you got the transformers.  Those oil caps, not sure I'd ever use them so figured I'd send them to someone who may.  And I still have a bunch left over!

If your asking me about the short rack power supply, no.  That was a different supply I built for someone.

The amp / supply that got me was built by someone else.  Incidentally, I've received another amp with a Killen connector.  Same problem.  Wire abraded going into the connector.  Idiots.

--Shane
KD6VXI


Title: Re: Another 813 Build
Post by: w9jsw on February 08, 2019, 07:24:19 PM
While I wait for the last relays to show up, I am going to knock out a pcb for the driver. Was never able to get hold of the guy that did the last one. Should not be too hard.

John


Title: Re: Another 813 Build
Post by: w9jsw on February 09, 2019, 11:28:43 AM
Separate thread for the Mosfet driver board. I am laying out a new PCB.

http://amfone.net/Amforum/index.php?topic=44619.0

John


Title: Re: Another 813 Build
Post by: Opcom on February 10, 2019, 01:45:45 AM
I've got that power supply in my shop.  Knocked me with 6kv.
--Shane
KD6VXI
How are you now BTW? I hope healed up well!!

I'm back working in the shop.  Cost me about 6 weeks of downtime but better than the alternative!  Dirt nap!

Glad you got the transformers.  Those oil caps, not sure I'd ever use them so figured I'd send them to someone who may.  And I still have a bunch left over!

If your asking me about the short rack power supply, no.  That was a different supply I built for someone.

The amp / supply that got me was built by someone else.  Incidentally, I've received another amp with a Killen connector.  Same problem.  Wire abraded going into the connector.  Idiots.

--Shane
KD6VXI

OK, I just thought that I might have the same transformer as in front of the short rack power supply, and wondered if it was used with a bridge. IIRC mine has three big ceramic terminals on the HV side and lightly stamped '5800' but I have to check. (of course it is on the bottom shelf with the business end facing away, and it's too heavy to be moved easily..) Also wondering what the transformer is from. I guess I should post a picture of it and ask in a separate topic, kinda mixed up as to where on here I saw it, thought it was in this 813 build topic but can't find it now.

Well as far as those connectors - if you insist on correcting that whenever found, future generations of people may live to thank you.


Title: Re: Another 813 Build
Post by: K1JJ on March 07, 2019, 10:00:47 PM
I came across this old pic of my Plexiglas 4-1000A modulated by 833As.  I had this thing about  being able to view the insides cuz we soon forget what it looks like once in a steel cabinet.  It worked pretty well but got transformed into Fabio II, the latest 4X1 X 4X1s. (in pics #2 #3)

Notice everything is on wheels or a pedestal - and EZ slip off enclosures for acccessible servicing.

A good excuse to check up on the progress of John's latest 813 rig...

T


Title: Re: Another 813 Build
Post by: w9jsw on March 08, 2019, 06:40:11 AM
Ordering a chassis along with the parts for the impending mosfet board arrival and going to start metal work layout on the rf deck. Have been conversing with Chuck to get the placement of the right angle turns and turns counters correct. My tank coil and band switch is huge so I plan to use a 17x17x4 chassis so I have plenty of room. I also picked up a La Pointe roller for the reverse Pi grid input. Now I need to find another multi-turn apparatus. Thinking of a vernier knob for this one. Needs to be smaller to fit right.

The buying never stops, it seems.

Where do I insert the grid bias in the filter? on the cold side of the roller? Where do I use a cap to block the DC - assume on the input to the reverse side and I should use a 500pf value? Do you perhaps have an example schematic?

Should I be planning on forced air flow into the chassis bottom and plan to make openings around the tube sockets to get air flowing up around the tubes?

John



Title: Re: Another 813 Build
Post by: K1JJ on March 08, 2019, 12:33:58 PM
Hi John,

I'll describe the grid circuit and then you draw the schematic and we'll go from there...



There are three paths, all starting at the 813 grid pins:


1) 2K > .001 cap to gnd

2) 2.5mH > .001 cap to gnd.    From .001 cap hot to grid leak resistor ... other side of GL >  .001 cap to gnd.   Hot side of cap >   -75V reg bias.


3)  .01 cap series >  300 pf variable to gnd.  Hot of 300 pF > roller inductor in series.  Roller other end> 1200 pF variable  to gnd.   Hot of 1200 pF > .01 coupling cap.   Other end of coupling cap is RF input.


No need for neutralization because the G-P is only 0.25 pF per tube and the 2K> .001 to gnd lowers gain to stablize everything. Good layout will help further.   Many have run 813s without neut with success.


Air cooling: Several possibilities:  Use heat-proof glass latern chimneys with holes around the socket. Squirrel cage pressurized from back or top of chassis. -  Underneath air pressure cools fil seals and glass envelope on top.   If no chimneys, then holes alone will suffice, but top plate seal is not cooled well unless a muffin fan directs air down from top at center of tubes in addition to air flow at bottom to cool fil seals.


If you can locate the proper size chimneys on the web, it makes a HUGE difference in overall cooling. I did that here and the 813 tubes show their appreciation by losing their blush... :-)

T



Title: Re: Another 813 Build
Post by: w9jsw on March 09, 2019, 09:24:31 AM
I think I am 100% complete on the design, Tom. Check closely the latest grid changes.

I have incorporated all that I can think of and all of the great ideas offered on this board. The project scope is huge but the benefits will be amazing... Think about where this started with a simple 1700v, 350ma supply and a single 8000 modded by a pair of 811's. Quite a difference!

Items to note on this revision -

1. New Grid input circuit with no neutralization planned - will build it very tight and shielded from the output tank. Floating roller inductor (found a nice one!)
2. Mosfet board interconnect added with NFB tap
3. Separate control of Mod and RF CT's
4. Switchable RX only antenna - going to try a LOG on 160M - http://www.kk5jy.net/LoG/
5. Arduino sequencer board - 6 steps planned (need to design this)
6. Safe start PS input - will shut down automatically if the power blips
7. Frequent use of Russian SPDT Vac Relays (They look like Plankton from Sponge Bob Cartoon!)
8. Spark gaps (will need to finalize a design and placement)
9. Changed to use the Gates dual 10V filament transformer.

I have all of the parts except the chassis and relays. I think I am finally ready to start! (measure twice - cut once analogy appropriate here)

Paper is easier to change than metal.

My PS will be started later. I am still mulling over the final enclosure. The rack that I might get from work only allows a 17in by 17in space. That is not enough space to cram all of that Gates iron into it without a lot of KY Jelly. I don't want to cram it in and have arching issues if a darn spider decides to make a web inside. A Gates enclosure is quite spacious in comparison.

I am going to start on the RF deck first. It will be on a 17x17x4 hammond chassis with I think a 10U front panel, with right angle drives underneath to the turns counters. The vac caps will be mounted vertically on either side of the chassis. Two tubes up front, with chimneys. Large Tank Band Switch and inductor behind the 2 tubes with the switch rod running between the tubes. Input tank vernier and knobs below.

Face will have meters across the top, tube viewing oval holes with the TBS knob in between. With chimneys, may skip the holes since the tubes will not glow much. Input tank controls south of the BS in the center, Plate and load outside on the same axis as the input tank.

I think that is it! Any comments or suggestions will be readily accepted.

John


Title: Re: Another 813 Build
Post by: w8khk on March 09, 2019, 10:34:22 AM
Looks good, John...

Just a couple questions regarding your schematic....

The plate current meter in the 813 Final cathode (filament) circuit will read combined plate, screen, and grid current.  You may want to consider floating the positive return of the control grid supply, as well as the negative side of the screen supply, and returning them to the center tap of the filament transformer.  Alternatively, you may float the negative side of the high-voltage supply, and place the meter between the supply and ground such that the 1000 mA meter reads only plate current.

You might also consider a higher voltage rating for the blocking cap coupling the plate circuit to the output tank.  5KV seems a bit marginal.  I use a pair of Sprague 20DKT5 caps in parallel, 500 pF each at 20 KV.  One may be sufficient.  Consider the capacity in parallel with the output of your modulator and its effect (in addition to the plate supply bypass capacitor)  shunting the higher audio frequencies when sizing this capacitor.

I do not see any protection for screens, should you lose plate voltage or excitation.  Perhaps some logic that requires drive and plate voltage before enabling the screen supply, or maybe a clamp circuit?  If screen supply is present without plate supply, the 813s will be very short lived..  GL on your project.


Title: Re: Another 813 Build
Post by: K1JJ on March 09, 2019, 12:13:08 PM
John,


Hey cool.... this is my post 7777.   Lucky mega-jackpot!  Where do I pick up the cash?
;D

OK on all. That rig is certainly turning into a professional project!   Now if you can maintain the workmanship at the same high level, you will be in the rare category of having a rig worth MORE than you spent on it...   Unfortunately, our time is usually way below minimum wage.  ;)

As Rick said, there's no screen protection. The modulators are OK since they are triode connected, but the RF finals will be at risk. Some guys chance it and are careful, but I prefer SOME kind of scheme to protect us from dumb mistakes.  In my 4X1 rig, I used robotics industry magnetic sensors that could be adjusted for current to trip a latching relay that opens the PTT circuit.  The shutdown delay speed is not as important with tubes as it is with solid state. Tubes can take more abuse for a second longer, usually, so mechanical relays are OK.   SS devices are milliseconds or less to damage.  

I used these magnetic current sensors in series with each DC circuit for the plate, screen and grid circuits for both of the RF finals and tetrode modulator tubes. So now if one of these tube elements goes past my preset limits, the PTT circuit opens up. (the fil CT opens so no current will flow thru the tube at all) It's kinda slick. I could come in drunk, turn on the rig and not blow things up... ;D   Do a search for current sensors and see what you find. It's easy enough to design using the sensor and a latching relay which opens up the 24V keying PTT circuit with a set of contacts.

The screen clamper circuit will work FB too.  Yes, 5KV for the plate coupler cap is a little low. Go for 10KV or more.

Your grid input circuit looks OK on the new schematic.

BTW, you don't have to use a tube, VR75, for fixed bias grid reg. A SS 70-80V  10W+  zener will work too.  This regulated voltage is to keep the grid bias filter cap from charging/ creeping up due to RF rectification. When testing, be sure this fixed bias stays solid with a full RF carrier. If it rises, I have a simple two component fix if needed.


When using the 813 chimneys, the drilled chassis holes around the socket base increase the chimney airflow.  Another way is to use spacers to make a gap so that there is 1/8"-1/4" recess of the sockets. This way no drilled holes are needed and the gap lets the air thru. The tube is designed for no pressurized air required so anything you do is a bonus to cooling effciency. As long as some air passes by the fil seals you are OK.

You can monitor plate current either by mentally subtracting the grids and screen current (as I usually do) or do as Rick suggests and float things.  The plate current meter in the negative lead is FB too. It's all up to you.

I'll look closer at the schematic later, but I think you are getting close to a workable build soon. The others here will hopefully see some more improvements or mods to make.

***  The mod reactor cap (C1) should be more than 3KV. If you can find another cap, put it in series for 1 uF @ 6KV.


T


Title: Re: Another 813 Build
Post by: w8khk on March 09, 2019, 12:44:23 PM
John, here is an example schematic (from Jun 56 QST) that shows how easy it is to place the plate current meter in the negative supply return instead of between the final cathode (filament) and ground....  All of course better than the old way of putting it in the positive plate supply lead - (ouch).  The 5 to 10 ohm 50 watt resistor ensures the negative supply connection is not broken, even if the meter is disconnected or fails.  The resistance is high enough that it will not significantly affect the meter reading, even though it is in parallel with the meter.

It also shows properly-sized caps for the plate coupling and bypass.  Hope this is helpful to you.


Title: Re: Another 813 Build
Post by: KD6VXI on March 09, 2019, 05:11:17 PM
I'll add, always but ALWAYS use a couple to a few 6A10 or 10A10 diodes from b- to ground.

They will clamp if that resistor opens up, preventing the chassis on the rf deck from approaching b+ value.

With a 400A surge rating they will take a lot more current than the meter and / or a 50 Watt resistor.

I size mine so the V Drop across them is the same as what is needed for plate current, then add one or two more to ensure they do not effect the plate current reading.

If you use inky enough diodes to pass said voltage, you start having the diodes conduct and pass current effecting the meter.

Try it on a small variable supply.  Two diodes in series will start passing current before 1.2 volts.

I've had to throw a LOT in series to repair / safe off others amps.  I had a 500Z amp come through here with all beautifully matches Simpson meters.  Except the HV plate current meter was in the b+ lead, causing 4kv to be present between the meter internals and ground!

Moved the meter to the b- side.  Took 11 diodes in series to prevent any diode clamp action effecting said plate current reading.  BUT if that meter opened up, their will only be 7 or so volts from ground to rf deck.

--Shane
KD6VXI


Title: Re: Another 813 Build
Post by: KK7UV on March 09, 2019, 05:26:47 PM
It appears that a meter in the HV- lead will read both PA and modulator plate currents on the common supply as John has.



Title: Re: Another 813 Build
Post by: w9jsw on March 10, 2019, 08:59:15 AM
ok on the higher voltage ratings. I actually have 20K and 30K doorknobs as well as some ruskie doorknobs that are 30K. I will update the schematic. Tell me more about the audio passthru. I have 4 500pf's and 2 470pf's to choose from.

The reactor cap is marked 3kv but it is the actual cap that came out of the gates so my guess is that is the working DC voltage not the peak. However,  that is the only component that I now have from the Gates that seems marginal in rating, so I will do as you say and add a twin. Safer approach than trusting an engineer's decision back when I was born (mid-50's). I have more risk than he does if it blows, I am sure!

On the screen, have doubled the plate relay to also turn on the screen. If HV happens to be present with the screen and plate off, what can happen?

We need to discuss the metering better. I understand all that was said but agree that putting it in the HV- will now read both plate and mod. The bigger issue is that changing the bleeder configuration breaks my compatibility with using the HV supply with my L4B. If I am going to add this I need to do it on the RF board only. Thinking.

I floated the screen and bias returns.

I have to rewire the filament supply feed from the controller. I have not looked yet but am sure the Gates fil trans will be 240V. Also, may need to buck it or add a variac to get it to exactly 10V. Going to add a filament voltage meter.

With all the relays and the variacs, I think am building Dr. Frankenstein's lab... Sparks a'flying and relays a'clacking!!!

John


Title: Re: Another 813 Build
Post by: K1JJ on March 10, 2019, 12:57:36 PM
It appears that a meter in the HV- lead will read both PA and modulator plate currents on the common supply as John has.


Steve,
Yes, you are correct. Good observation.


I think John now has the metering all independent in his latest schematic by floating the negative for the grid and screen supplies  - and then keeping the plate current meters in the fil CT leads for the plate mod and plate RF.  That should all work FB now unless I am missing something. For each solution there seems to be a disadvantage but this is a good compromise now.


John, what do you mean by "audio passthru" caps?  Maybe you mean limiting the plate bypass and plate coupling caps to 500 pF max so that the extreme audio highs are not shunted too much.  Then yes, keep them 500 pF or so. Remember that the pi network has 1300++ pF to ground at times and that plate coupling cap is the only isolation from this being part of the mod xfmr audio circuit.  The smaller the better, as long as it works OK for RF..


Your question:   "On the screen, have doubled the plate relay to also turn on the screen. If HV happens to be present with the screen and plate off, what can happen? "

HV and plate are the same thing to me, so not sure what you mean.  But if the HV is on the tube, PTT keyed or not keyed in the fil CT, fil voltage on or off, screen off, then no problem.    The only problem is when there is screen voltage on, fil voltage on, PTT keyed, HV off.  This will cause excessive screen current and do damage.   We should probably make up a matrix table showing various voltages on or off, PTT keyed or off, fil voltage on/off to show all of the possibilities. But once you sit down and think it out, you will have a better understanding of the risks and what you should not do.


But the risk still remains... even if you have sequenced screen voltage keying, what happens if you are transmitting and the plate supply fails for whatever reason? Your screen current will soar and possibly do damage to the tubes before you are aware enough to unkey the PTT. That's why a current sensor or clamp is required in the screen circuit.  Accidents can happen to the grid circuit too but to a lessor degree.  

Once you get the rig running, you can carefully try different scenarios and see just what you can get away with and not.  IE, key the PTT, slowly add a tiny amount of screen voltage with the Variac and apply a small amount of drive... Turn on HV and see what happens, etc.

All of this is akin to driving a dragster. There is nothing automatic and safe about any of it. There's a lot of knobs and adjustments and easy to get into trouble when trying to make them all work together smoothly.

You continue to do a fantastic job putting this all together, John!!

Did I cover everything for now?

T


Title: Re: Another 813 Build
Post by: w9jsw on March 10, 2019, 04:18:03 PM
ok, Tom, great explanation. So screen is not an issue unless the plate disappears, right? Then the screen becomes the plate and bad stuff happens quickly. So I really don't need to key the screen. Just have a clamp on it that activates if I lose HV, right? Is it that simple?

John


Title: Re: Another 813 Build
Post by: K1JJ on March 10, 2019, 05:06:03 PM
John,

Yes, this is correct.

Essentially, if the HV and screen are both always on, or get sequencer turned on or get turned on together, no current will flow anywhere until the fil CT is grounded with the PTT relay contacts.

So everything will work FB until you lose the plate voltage by accident while the PTT is on.  Then the screen magnetic current sensor or screen clamp circuit takes over.  The sensor will break the PTT control line so that everything sequence cycles off.  You COULD also have a direct path from the magnetic current sensor to the screen DC circuit to break it so it occurs faster, outside of the PTT sequencer rotation.  

Or an all-electronic screen clamp shutdown circuit would be the fastest of all.

There's many options here.

T


Title: Re: Another 813 Build
Post by: w9jsw on March 10, 2019, 09:47:43 PM
I get it. I am planning to use the Arduino for sequencing. It can also read some current sensors and convert it from A to D. I can have set points that then override the sequencer to drop the whole shebang in an orderly fashion. This could be pretty cool.  8)

I think I may even have to find some room for a 4 Line LCD display. My DDS is already being run by an Arduino and has a Freq display.

John


Title: Re: Another 813 Build
Post by: K1JJ on March 10, 2019, 10:55:43 PM
Sounds slick, John!

When I have a fault in any of my six current sensors, hearing the sequencer cycle down in an orderly fashion is a thrill.  I use latched LEDs to identify which tube element caused the problem and a master reset button to try it again.


I have a question for the group related to the screen clamper, etc.  

**Update:  Never mind - question answered offline.

T


Title: Re: Another 813 Build
Post by: w9jsw on March 17, 2019, 10:44:45 AM
Chassis on order.

What is a good rule of thumb on how deep to make the decks to fit in a standard rack? The Motorola rack I had my eye on is just too small. Only 17in deep. I really need to make the PS and the Mod deck around 17in x 20in or so. The mod deck will have a 17x10 front chassis for the tubes and mosfet driver. It will set on a wood platform that has space in back for the mod transformer, mod reactor and reactor caps. I think I can get them to fit in 10in of space or maybe a bit more. The PS is needing a wood platform of about the same 17x20 or so. A few more inches would be even better. How about 17x24in?

Looks like the Lehman FLG globe will work for the chimney unless anyone can suggest a different one. How do you attach them to the chassis? Price is now up to $6.95, not too bad.

John


Title: Re: Another 813 Build
Post by: K1JJ on March 17, 2019, 12:59:15 PM
Hi John,

The boards arrived and are beautiful - thanks!

Here's the link to the "813" chimneys for the other guys. They look like the ones I used. Great price for temperature-rated glass. They can be secured to the chassis like chimneys made for 3-500Zs, etc. Some kind of clips that have spring.  Three or four clips in a circle will do.  Look around and you will find something that will work, even if they are the expensive Eimac clips. Put your blower motors on a Variac and you can set the air flow to a very quiet level but still cool FB.

If you sub-mount the 813 tube sockets by 1/4" or so, you will have a good breeze thru the chimneys. No need for air holes in the chassis.

https://www.lehmans.com/product/clear-globes-for-dietz-blizzard-lanterns

As for the cabinet depth, that really depends on what you can find. I have always been very grateful when I find a DEEP cabinet. The extra depth always gets used.  Even if not, the extra room for working and better ventilation is FB. Very few hams ever complain about having extra space in any situation... ;D  My cabinet for Dr. Love is 30" deep. Even 36" would be FB.

T

Dr. Love:  Notice the trap door when I used plug-in coils. Dr. Love now has a big bandswitch.  Look closely and notice the fiberglas air ducting for the cooling outside. That has since been chaged to a sub-chassis blower with a Variac.

My all-time favorite color combination has been a white panel, black lettering, with a "blue IBM"  cabinet.  

Below: The days of wine and roses... and sweet memories.


Title: Re: Another 813 Build
Post by: K1JJ on March 17, 2019, 03:20:41 PM
John,

Since you're still on the quest for a rack....

It makes a big difference in accessibility by having the rack side panels easily removeable. This includes the rear door, if any.  You can actually lean in and work on the rig when the side panels are removed.  Some racks do not have removable side panels, so be sure.

Also, be sure to have a bracket or shelf that supports the bottom of each rack panel. Most racks have brackets and/or mounting holes to start the process.  Holding the chasis up by only the 19" rack screws is NG. You will be axing the XYL for help unless you are Dick the Bruiser.

Better yet, if you are really smart, get some of those 19" rack slide in/out assemblies that lets you work on each 19" unit out in front of the rack.  Just be sure you have plenty of weight in the bottom of the rack or low enough C.G. to prevent rack tipping.

Make sure the wheels are extra heavy duty AND the wheel brackets holding them to the rack are extra strong and well reinforced. I actually had a rack NEARLY fall over in the shack when one of the front wheel brackets collapsed.  I caught it in time and had to wrestle it into a safe position. The biggest stress is when you are moving the rack over uneven or rough floor, rugs, etc..

Be sure the height fits into a room with low ceilings... or lower ceilings in the future.  (crystal ball)

Paint it to perfection as soon as possible, before you start putting stuff in. Otherwise it may never get done.

T


Title: Re: Another 813 Build
Post by: W2PFY on March 17, 2019, 03:37:52 PM
Quote
John,

Since you're still on the quest for a rack....

Me too! I wuz doing that in WallyWorld today and almost got thrown out for gawking??


Title: Re: Another 813 Build
Post by: w9jsw on March 17, 2019, 03:48:17 PM
Quote
John,

Since you're still on the quest for a rack....

Me too! I wuz doing that in WallyWorld today and almost got thrown out for gawking??

always a wise guy in the crowd  ::)


Title: Re: Another 813 Build
Post by: W1RKW on March 17, 2019, 05:04:41 PM
I have an enclosed rack that I acquired from Joe/WB1AIU which is the home of GORT.  The rack is 4.5ft tall and is 24 inches deep. I mounted it on heavy duty wheels. Between the rack and the hardware installed in it, it's about 250lbs. It has 19" rails both in the front and in the rear.  I took advantage of of the rear rails by installing perforated angle iron between the front and rear to be used as sliders for the 4 chassis support sections of the transmitter. There are 2 chassis's with transformers and there is no way that the front panel of each chassis will support itself let alone trying to install and remove those chassis's by removing and installing the mounting screws. That would take to people.   The rails provide support and unstress the front panel and I  am able to remove/install each chassis by myself.  


Title: Re: Another 813 Build
Post by: w8khk on March 18, 2019, 08:03:21 AM

I have a question for the group related to the screen clamper, etc.  

**Update:  Never mind - question answered offline.

T

Tom, after thinking about your question and because I did not arrive at any valid hypothesis on my own, I refrained from commenting prematurely.  But I (and possibly others) would  like to hear what you learned offline about the behavior of the screen grid voltage and current when using the combination of fixed and grid-leak bias as the grid current changes.  (I was out of town for a few days, hence the delay in my comment.)

Thanks in advance for taking the time to elaborate!


Title: Re: Another 813 Build
Post by: K1JJ on March 18, 2019, 08:37:17 PM
Hi Rick,

Actually I wasn't really satisfied with the answer I received and didn't want to waste any more time on it.  I decided the next time I fire up the 4X1 rig I will see for myself exactly how the screen current responds to grid drive as the grid leak bias increases.  It eventually settles at 280 mA with full grid drive and with the Variac-driven screen voltage adjusted right, but the path it takes to get there, I don't remember... :-)

T


Title: Re: Another 813 Build
Post by: w8khk on March 18, 2019, 09:31:56 PM
Thanks for the explanation, Tom. 


Title: Re: Another 813 Build
Post by: w9jsw on June 16, 2019, 07:58:39 AM
Finally! I am in possession of my rack. Is an old Motorola comm rack. Built very well. Has some nice stainless louvers on the bottom that will really help air flow - and look super. Needs a good cleaning.

I have stripped off the sides and the front (now back) door. I positioned the rack bars so that the transmitter will have the faceplates flush with the now front line of the rack giving me a whopping 17x17in space to mount the mod and RF chassis. I had bought a 17x17 one but now will trade it in on a 17x15 one. Glad I was not premature on cutting on the chassis. This will be a bit tighter but will give me room for cables on the back of the chassis and still be able to close the door.

Putting in a 3/4in plywood floor and casters to allow easy movement. First task is to position all of the iron for the PS components on the wood floor. I may have to do a double decker for some parts like the caps. Gates had all of the iron on the floor of the rack. Having the sides off will make this build much easier. I am using 5/16 bolts and t-nuts to make the iron solidly attached to the unit. I have 175lbs of iron to mount. Casters can handle 600lbs of weight. I am thinking I will be in the 400lb ballpark when finished. Heavy metal baby!

I will then start on the power control chassis. Then modulator and last the RF deck on the top. Included the schematic for anyone following along.


Title: Re: Another 813 Build
Post by: w4bfs on June 16, 2019, 01:09:23 PM
ain't nuthin like a big homebrrrrrew project ! :D :D   like the new avatar as well


Title: Re: Another 813 Build
Post by: w9jsw on June 16, 2019, 01:42:43 PM
Was on the shore of Lake Erie with a microbrew in my hand. One of my better days.


Title: Re: Another 813 Build
Post by: w9jsw on June 16, 2019, 02:54:32 PM
A big homebrew is a bit like this game

https://en.m.wikipedia.org/wiki/Three-dimensional_chess

Just about popped a nut just moving them into position. Definitely going double decker!

Think I will put a layer of aluminum between the wood and the iron. Better ground for all the iron and no visible combustibles. Overthinking this?

John


Title: Re: Another 813 Build
Post by: KL7OF on June 16, 2019, 05:25:49 PM
Yes overthinking...Old Iron is actually better mounted on wood..Frames not at ground potential....IMHO


Title: Re: Another 813 Build
Post by: w8khk on June 16, 2019, 05:37:28 PM
Yes overthinking...Old Iron is actually better mounted on wood..Frames not at ground potential....IMHO

Yup, that is the way I do it too.  No need to bolt 'em down, either.  Just place them with reasonable clearance, and they will stay put, even with the rack on casters.

In my 250TH rig, I used an HP 5KW isolation transformer.  it had a slight hum, even on the wood, so i placed it upon a one-inch thick slab of styrofoam, quiet as can be now. 

By the way, when I was about five, my dad was fixing a radio for me.  It needed a new filter cap.  But when I asked him why it hums, he just said "because it doesn't know the words."


Title: Re: Another 813 Build
Post by: Opcom on June 16, 2019, 07:15:21 PM
Wood is good! 3/4" is a bit thin for 'no flexing' with that heavy stuff there. Probably 2x6 or 2x10 planking is more than enough to make a great floor and will just fit side to side, depending on the rack.

Personally I like to secure the iron in place and do not understand why people like to have it loose, just set in place. To ground or not to ground? depends on the parts and safety concerns if someone else ever has to work on it.

Planks let you run 1.5" x 1/4" or 3/8" lag bolts into them to fix the iron in place yet be able to remove it easily with a 7/16" socket if wanted. Fender washers under the bolt heads keep from scratching the transformer frames.

A piece of angle iron across the planks at each end hold the 'crack' together great. I did it a little different, running transformer bolts into the angle too, but that floor is solid due to the angle iron and nothing is going to move.

Overkill? maybe, but we should each do what makes each of us happy!

Just thinking long term because this kind of equipment you are building could last 50-100 years if done right.

p.s. don't use water-resistant/pressure treated wood. The chemicals can slowly corrode metals.


Title: Re: Another 813 Build
Post by: KD6VXI on June 16, 2019, 10:28:13 PM
Yes overthinking...Old Iron is actually better mounted on wood..Frames not at ground potential....IMHO

I was called nuts for stating frames should be isolated.

--Shane
KD6VXI


Title: Re: Another 813 Build
Post by: K1JJ on June 17, 2019, 12:40:03 AM
Hola John -

After a brief interlude, you are back.  I also like the new mellow avatar.  You look like a salty dog on the sea..  ;)

Paint the rack a nice IBM computer/ blue like below..

As for big iron mounted on wood, I have always done this with mod xfmr, chokes, Heising caps, HV power transformers, etc.  The practice simply keeps an old transformer from risking it's frame to wire insulation rating.

The only downside I see is a safety risk in case of the slim chance that one of the internal wire turns touches the frame/case after a blow out and puts the frame and case at full potential. (Or the wire to frame insulation simply fails)  I've had a Heising cap, 5 KV @ 2 uFd once internally short to the case and make the case hot for HV.

Any thoughts on this?


BTW, how do you get "Two shots of whiskey" from JSW?   Is that AFTER drinking a whole bottle?

T


Title: Re: Another 813 Build
Post by: w9jsw on June 17, 2019, 06:35:51 AM
Whisky 9er Juliet Sierra Whisky - sound it out.

Having a hot frame on the iron worries me. I think I would want it to blow the fuses if a short developed. Look at the other side - you have a transmitter that continues to operate but you now have a risk of fire if it starts to arc due to anything bridging the frame to ground - perhaps a mouse or something. Or you fiddling where you should not and touch a frame that you THOUGHT should not be live. I think I want it grounded. Convince me otherwise...

John


Title: Re: Another 813 Build
Post by: w9jsw on June 17, 2019, 12:29:14 PM
Or is the idea that if you float the frame on a 60 year old transformer it will make it less likely that it will short.


Title: Re: Another 813 Build
Post by: K1JJ on June 17, 2019, 02:59:59 PM
Yes, that's the idea.

It's safer to ground the frame so that if the insulation fails, the HV fusing system opens and kills the HV source.

Though, there are lots of exposed HV points in the rig and if the HV power is on we have no business touching anything inside anyway.  IE, whether we touch a hot transformer case or the HV diode stack, we get zapped.

I personally prefer to float the iron on wood or Plexiglas and never touch anything inside the cabinet when the HV power is on.  Always act like the transformer case is hot. We could make up a Plexiglas enclosure to put over it, I suppose.

"Whisky 9er Juliet Sierra Whisky - sound it out."  I see two whiskeys, but how does 9er Juliet fit in?


T


Title: Re: Another 813 Build
Post by: KD6VXI on June 17, 2019, 05:14:23 PM
If you really wanted to be safe from a shorted frame, tie a resistor to the frame of the isolated xformer / choke and use ohms law to drop it to 120 volts (or 24, depending on the trip voltage) and hit a shunt trip breaker.

That will keep the breaker from staying live under any circumstance darn near.....  Even if you lost ground connection to the chassis somewhere/how.

This is how electric is cut during a fire or other event in commercial and industrial electric.

--Shane
KD6VXI


Title: Re: Another 813 Build
Post by: Opcom on June 18, 2019, 03:34:43 AM
If wood is used for a floor, then a heavy jumper can ground the transformer frame to the chassis or the protection scheme can be used. There are always options.
The pictures were only to show what I thought was a great way to make a real strong floor in a rack at almost no cost.

In my 1950's 4-1000 homebrew rig, everything is grounded to the cabinet but the mod transformer, because that item is very ratty and from the 1940s. The rest of the stuff was new at the time. The original builder did not ground the mod iron because he was sometimes running 5KV in there. When I put the thing back together I rewired the HV supplies to make only 3300V.

When designing and building something new like in this topic, there's a perfect opportunity to put the low voltage and control circuits well away from the high voltage parts in case some work has to be done.


Title: Re: Another 813 Build
Post by: w9jsw on June 18, 2019, 06:57:53 AM
ok, got it.

HV gets assembled this weekend.

What do you all use for a HV probe? I am thinking of buying the BK 28A one.

https://www.amazon.com/Precision-PR-28A-Voltage-Attenuation/dp/B004PA02Q8

John



Title: Re: Another 813 Build
Post by: Opcom on June 19, 2019, 01:04:53 AM
That one would be great for ham radio work, just use a lower scale on the meter. I see it has a ground clip. That's the safety feature as well as the tapped multiplier return.

No matter what kind storebought or home made, I never like to hold them while measuring, but I'm shy after being hit by a color TV set because of a faulty probe.

Some of the TV set types like that 40KV unit on Amazon used to come with a slip-on spring hook that let it hang in place without being held.


Title: Re: Another 813 Build
Post by: DMOD on June 19, 2019, 01:26:21 PM
ok, got it.

HV gets assembled this weekend.

What do you all use for a HV probe? I am thinking of buying the BK 28A one.

https://www.amazon.com/Precision-PR-28A-Voltage-Attenuation/dp/B004PA02Q8

John


I have that same probe and found it indispensable when probing HV circuits.

I used it a lot when checking voltages on the HV circuits in my 813 based 175 watt Screen Modulated, 3-band, homebrew transmitter, which had an HV B+ of 2,200 Volts.

 
Your build would make for a great article for Electric Radio magazine.  8)


Phil - AC0OB



Title: Re: Another 813 Build
Post by: w9jsw on July 04, 2019, 04:06:54 PM
Progress...

Have the front panel laid out to mount the power switch, breakers, HV Meter and the honk'in powerstat. Time to make some holes. Power switch is one of those NC/NO ones that works in conjunction with a 3PDT relay to have the power shut down completely if there is a mains glitch. Will also have my back door interlock in the circuit so that if the door gets opened, it all shuts down.

All the iron mounted. Tight.

Working out where to place the big caps and the relays. I think the caps will mount on a side shelf strapped to the side of the rack. A similar shelf on the opposing side to hold the 3 relays. I think that will work. 

Do the magnetics generate much heat? Mod trans and mod reactor are pretty close. Can move them an inch or so if necessary. Those are the two in the back - L3 and the white tag one.

Glad I have 6 feet of rack to work with. The plan shows it all fitting with a 3U space left over. Thinking about a 3 fan spacer and running the fans at 1/2 voltage. The bottom of the rack has stainless louvers so that should create some good airflow and hopefully not be too loud.

John



Title: Re: Another 813 Build
Post by: Opcom on July 06, 2019, 06:30:40 PM
Not to pick, but laminations are facing same way on power and audio iron -but it's not a preamp being built after all!

Looks like it will all be grounded, so close-in but it's fairly new iron. Doubt you will really have any shorting or heat issues. I think it's great! Love generous power supplies.

Nice big Variac as well. Have a shot of Red Cat to celebrate!


Title: Re: Another 813 Build
Post by: w9jsw on July 07, 2019, 06:46:06 AM
Still fiddling with the layout.  ::)

Changed orientation of the mod trans and mod reactor to make more floor space. BTW, floor is 2 sheets of 3/4 in plywood. Plenty stout and give me an ungrounded mounting platform. Also bought some insulated terminal boots to allow me to cover up all of the connections to insure no possible arcing in the future. White wire is 20kv rated, red wire is 30kv rated. Diode string is mounted on polycarbonate with a insulating sheet below. White posts are for the HV fuse. All caps will be secured once I finalize the plan.

Option 1 fits all of the caps on the floor, but I lose one of the large caps so I go from 64uf to 32uf on the PS caps. 32uf is still 4X what the Gates had which was 8uF.

Option 2 maintains the 64uf of PS caps but I then have to place the reactor caps up high on the side of the frame. Longer leads on the caps which I generally do not like.

Which would you do and why?

John


Title: Re: Another 813 Build
Post by: K8DI on July 07, 2019, 08:17:58 AM
Being pessimistic, but what about serviceability? If you mount the iron and caps like that, how do you probe anything, let alone change taps or remove one of the transformers, without taking it all apart?

Ed


Title: Re: Another 813 Build
Post by: w9jsw on July 07, 2019, 10:46:51 AM
Hi Ed,

With option 2, I can probe all of the taps on the mod iron. Option 1, not so much, so perhaps I will go with option 2. The taps for the PS are on the front and top and can easily be accessed by removing a louver, or reaching in the back with the door open. The next item in the rack will be a PS chassis for the bias supplies. It will be a short chassis that still gives me space to safely probe. As to removing the transformers, they are easily removed with the sides off. I used t-nuts and bolts to hold them down. Easy nutdriver access to remove the bolts.

Given that this was the only rack I could find, have to make do. It would really be nice to have 6 more inches of space. It will still be easier than changing an alternator on one of our cars.

Thanks for the comments.

John


Title: Re: Another 813 Build
Post by: w9jsw on July 07, 2019, 06:27:32 PM
Progress...

The meter is special. I don't recall where it came from. I have had it since I was a kid some 50 years ago, probably a ham-fest. I had it in a single meter enclosure and it has knocked around with me since college or before. I had set it up to be a 25V dc meter. I really needed to use this meter on this project...needs cleaning.

PS front panel laid out. No indicator lights as the Off-On SW lights up in the center. I need a power stat metal disc. Anyone have one laying around?

I think I finalized the iron footprint, baring any unforeseen obstacles that you guys point out. See anything odd or out of place?  ;D

John


Title: Re: Another 813 Build
Post by: K1JJ on July 07, 2019, 06:38:26 PM
Hi John,

Looks robust!   You are a trooper working into the hot summer when many take a building break.


Question: Maybe it's an optical illusion, but how much space is between the bare HV diode leads and the plate transformer iron?   Dust, moisture, sharp edges, corona, reactor collapsing fields, etc., can cause arcing greater than the normal 1/2" = 10KV standard.  I would have at least 1" of space there.  Or, a Plexiglas plate placed under the diode board would suffice.


T




Title: Re: Another 813 Build
Post by: w9jsw on July 07, 2019, 06:49:45 PM
There is a Plexiglas plate there... Your browser may allow you to zoom in to see it.

You know, a lot of guys would like to have this problem. This is some serious kick a** iron that Phil sold me.  8)

This is being built in my basement. So nice and cool down there. Kind of like building a yacht in the basement. Won't be my problem to get it out of there... My goal is to be doing trials in the fall/winter.

Has Yaz been taking you sailing this summer? Where do you usually go? Salt or fresh?

John
AMfone - Dedicated to Amplitude Modulation on the Amateur Radio Bands